The proposed work will be centered on the structure and function of lys-tRNA4. This lys-tRNA is of interest because it has been correlated with cell division. Further attempts will be made to isolate this and other isoaccepting lysine tRNAs so that the modified base content of these tRNAs can be determined. We intend to continue our studies on the effects of culture conditions on the levels of lys-tRNA4 with various cell culture lines. This will hopefully indicate whether certain factors are required to maintain high levels of this lys-tRNA. Since lys-tRNA4 is the highest in a transformed mouse leukemia cell line, we intend to look at the lys-tRNA population in an RNA tumor virus. We are particularly interested to see if lys-tRNA4 is specifically bound to the 70S RNA of Avian Myeloblastosis Virus. It seems likely that this tRNA could act as a primer and be required for virus production.